Structure-design and synthesis of nickel-cobalt oxide/sulfide/phosphide composite nanowire arrays for efficient overall water splitting

The construction of cost-effective bifunctional electrocatalysts with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for efficient overall water splitting. Herein, this work demonstrates a novel strategy for the synthesis of nickel cobalt oxides/sulfides/phosphides composite (denoted as NiCoO-2P/S) nanoarrays on Ni foam. In this method, Ni-Co bimetallic oxide nanowires on Ni foam were partially phos- phorized and sulfurized simultaneously in situ to yield Ni-Co oxide/sulfide/phosphide composite. The NiCoO-2P/S arrays have good interfacial effects and display many holes in the nanowires, giving it the advantage of large accessible surfaces on the nanowires and a beneficial for the release of gas bubbles, resulting in an excellent OER performance with a low overpotential (h) of 254 mV at 100 mA cm-2 and good HER activity (h10 = 143 mV at 10 mA cm-2). The electrocatalytic test results demonstrate small Tafel slopes (82 mV dec-1 for HER, 88 mV dec-1 for OER) and the satisfying durability in an alkaline electrolyte, indicating that the HER and OER activity was enhanced by the introduction of the Ni/Co sulfides and phosphides into Ni-Co oxides composite nanowires. Furthermore, the as- prepared NiCoO-2P/S catalyst can be used as both the anode and the cathode simulta- neously to realize overall water splitting in the two-electrode electrolyzer. This system can be driven at low cell voltages of 1.50 and 1.68 V to achieve current densities of 10 and 100 mA cm-2, respectively. This work provides an alternative strategy to prepare high- performance bifunctional electrochemical materials and demonstrates the advantages of Ni-Co oxide/sulfide/phosphide composites for water splitting.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.